Continuous wave (CW) radar systems offer certain advantages over pulse radar systems. Even so, CW radar systems suffer from a disadvantage of a strong direct path signal being coupled between the transmit and receive antennas. The direct path signal can result from imperfect isolation between the transmit and receive antennas as well as from scattering from nearby objects. The direct path signal can be several orders of magnitude larger than the received signal of interest and therefore tends to hide the received signal. As a result, the direct path signal can reduce the sensitivity of the receiver. With reduced sensitivity, the maximum range of the radar is reduced.
One solution for reducing the direct path signal has been to separate the receive antenna from the transmit antenna. This provides better isolation between the transmit and receive paths. However, even relatively small side lobes in the transmit and receive antennas will result in coupling that allows leakage signals to occur. In addition, scattering from nearby objects can still result in a significant direct path signal received at the receiver.